1. Field of the Invention
This invention relates generally to cable television communication system distribution components. More particularly, the invention relates to a passive signal component that obviates standard CATV power inserters by permitting power insertion or extraction in either direction of a bidirectional cable television communication system.
2. Description of the Prior Art
Many different types of cable television (CATV) communication systems exist providing a large diversity of services. Conventional one-way CATV systems primarily provide broadcast video services, which are sent over a CATV transmission network in a downstream direction, from a headend of a CATV network to a plurality of subscriber terminals. Bidirectional CATV systems allow subscribers to interact with their programming providers which have become commonplace in the industry as the diversity of services has grown. New services that are under development will rely on the full use and deployment of the return path communication.
The CATV transmission network usually comprises a trunk system designed for the bulk transport of the plurality of CATV services. Bridging amplifiers are used to feed signals from the trunk system to a distribution system, then onto individual subscriber drops.
A CATV transmission distribution plant includes coaxial cables, signal couplers/splitters, amplifiers, and subscriber taps. When placed in the signal path, passive transmission devices attenuate the signal. Normally, the system is designed with unity gain from the headend to each subscriber terminal, taking into account the signal losses throughout the trunk, branch lines and subscriber drops. As the signal proceeds along the distribution system, the attenuation of the coaxial cable and the burden of passive devices reduces the signal to a level such that amplification may be required. Line extender amplifiers, which provide the amplification, require a source of power.
The line amplifiers are usually suspended by the signal carrying coaxial cable support strand between telephone poles and are powered from the signal coaxial cable. Rather than distributing the power with separate power cables, alternating current is periodically inserted into the signal carrying coaxial cable via CATV power inserters.
A power inserter impresses the alternating current source on the coaxial cable without interfering with the RF signal. The power inserter houses a low pass filter for 60 cycle, 60 Vac and a band rejection filter for the RF signal present on the coaxial cable. The power inserter, namely the filter network, is located in a weather and RFI proof housing and is also suspended on the cable strand. Pole mounted ferroresonant transformers provide the reduction and isolation of the local utility power supply to the power inserter. The line amplifier separates the RF signal from the impressed 60 Vac with a low pass filter to rectify the current for use in powering the amplifier. A high pass filter passes the RF signal to the amplifier gain stages.
Rather than using a separate device for power insertion, it is desirable to include power insertion or extraction at the signal splitters.
To reduce the complexity of CATV distribution systems and further increase installation flexibility and overall performance, it is desirable to include more power insertion options in standard CATV signal splitters.